1. Field of the Invention
This invention relates to method and apparatus for suppressing dust and frictional ignition in the operation of a continuous mining machine and, more particularly, to a continuous mining machine having a cutter drum equipped with a rotary valving assembly for supplying water to the portion of the cutter drum where it is needed to suppress the generation of dust and the occurrence of frictional ignition.
2. Description of the Prior Art
In underground mining operations using drum-type continuous miners, cutter drums extending from the front of the machine are provided with cutting bits and are moved into engagement with the mine face to dislodge solid material therefrom. It is well known in the art to locate water spray nozzles on the cutting drum near each bit to suppress the generation of airborne dust and frictional ignition as the cutter bits engage the mine face.
Utilization of spray nozzles adjacent the cutter bits on the surface of the cutter drum has been found to effectively suppress dust before it becomes airborne. The water is continuously sprayed from the nozzles during rotation of the cutter drum, suppressing dust at the point where the material is dislodged from the mine face. Generating a water spray at the bits suppresses the dust at its source and effectively eliminates any risk of frictional ignition as the cutter bits strike the solid material. Generating a spray from the nozzles also serves to extend the life of cutter bits on the cutter drum.
Examples of mining machines equipped with cutter drums having dust suppressing spray nozzles are disclosed in U.S. Pat. Nos. 3,698,769, 3,876,254, 4,565,410, and 5,507,565.
With the above described spray devices, water is continuously supplied to the nozzles regardless of their position relative to the mine face. In many applications, it is necessary to conserve the amount of water used in the spraying operation as well as reduce the amount of mud produced by the combination of the dust and the water. Control of these features may be achieved by phasing the supply of the water to the spray nozzles. By phasing the water supply, only the spray nozzles positioned adjacent to the cutter bits engaging the mine face are supplied with water. Phasing of the water supplied to the spray nozzles can conserve as much as 50% of the water used for dust suppression during the mining operation.
A number of systems have been proposed for phasing the water supply to the spray nozzles. For example, U.S. Pat. No. 3,374,033 discloses a mining machine having a boom supported cutter drum in which a liquid inlet extends through each boom member from a pressurized water source. The water is directed through the inlet into a non-rotatable housing which supports the cutter drum. From the housing, the water flows through a non-rotatable annular valve ring. The valve ring is designed to permit water to travel through only a pre-determined 90.degree. arc corresponding to the point of contact between the cutter drum and the mine face. Thus water is supplied to only one quarter of the spray nozzles at any given time. A rotatable, annular port plate is connected to the cutter drum and includes ports through which the water travels to the spray nozzles.
U.S. Pat. No. 4,470,636 discloses a phased water delivery system for use with an auger style mining machine. Water is supplied through a stationary tube into a reservoir between a stationary tube housing and a rotatable valve body. From this reservoir, the water contacts a stationary annular valve plate which limits the water to advancing only through a predetermined arc. This valve plate is aligned with a port plate having ports each leading to a tube. The tubes, in turn, lead to nozzles which spray water onto the mine face.
U.S. Pat. No. 5,098,166 discloses a method of gearing a cutter drum which permits the center of the drum to remain stationary while the outer portion of the cutter drum rotates. Pressurized water is supplied from a stationary boom member into an axial bore through the fixed center of the drum. The water is conveyed to a stationary annular valve plate adjacent the end of the drum having openings along a limited range of its circumference. The valve plate lies adjacent to a port plate which rotates along with the outer portion of cutter drum. The port plate has bores therethrough aligned with passageways which lead to the spray nozzles. In this manner, the water is only supplied to the spray nozzles during a desired portion of the drum rotation.
Other examples of the use of water sprays to suppress dust generated during the material dislodging operation of a mining machine are disclosed in U.S. Pat. Nos. 4,389,075; 4,621,869; 4,721,341; 4,755,002; and 5,054,858.
With the above described devices, conventional seal rings are used to provide a rotary seal between the stationary and rotary components of the cutter drum. The large diameter rotary seals required for use with continuous mining machines must operate for an extended period of time in a dust filled environment to prevent leakage of the spray liquid into the bearings or the gearcase. Failure of these seals can result in costly damage to the cutter drum components.
The port plates in the above-described devices supply water only to the spray nozzles in one section of the cutter drum. Therefore, there is a need for a phased dust suppressing apparatus that minimizes inevitable damage caused by ineffective rotary seals.
There is further need for a phased dust suppressing apparatus in which spray nozzles on a plurality of sections of the cutter drum are supplied by a single phasing valve.